Abstract :
The present paper studies the problem of stable normal zones in a superconducting coil. It is shown that there are five solutions, namely; T1(X), T2(X), T3(X), T4(X), and T5(X), of the heat equatuon that describes a locally uncooled superconducting wire within certain ranges of currents and magnetic fields. Of the five solutions T1(X), T3(X), and T5(X) are stable, and T2(X) and T4(X) are unstable. Stable stationary solution T3(X) describes the short normal zones mainly located in the nucleate boiling range of the coolant. T1(X) is the superconducting state, and T5(X) having a longer region above the critical temperature than T3(X) generally is the quench state. Unstable stationary solution T4(X) describes the minimum propagating zones. Normal zones will develop if the temperature profile in the conductor is above T4(X); it will contract if the temperature profile is below T2(X). Stable normal zones in superconducting cooled by HeII are also discussed. It is easier to get conditions under which stable normal zones exist in HeII than in HeI. Using the theoretical model, a detailed numerical analysis is made that determines a range within which stable normal zones occur. Some experimental results are presented and compared with theoretical calculations.
